The present invention relates to a control apparatus and a control method for an AC electric motor.
In order to drive an electric motor highly efficiently, it is necessary to estimate a motor current flowing through the electric motor accurately.
In a technique described in Japanese Patent No. 3610897, current information for 2 phases is detected from DC bus current and a motor current is estimated on the basis of the detected value. However, the current information for 2 phases is obtained within a period of carrier and accordingly it is necessary to adjust switching timing of inverter. This adjustment increases an operation load of a microcomputer and noise.
In a technique described in JP-A-2007-221999, in order to solve the above problem, the motor current can be estimated on the basis of only current information for one phase. Instead, it is necessary to calculate an integrated value of the product of a detected value of DC bus current and a periodic function within a predetermined period in order to estimate the current once. At high-speed driving, since the number of times of detection within the period is reduced and the integrated value is not obtained exactly, the estimation accuracy of current is lowered. Furthermore, the current estimation algorithm contains the periodic function and accordingly operation load and calculation error are produced.
In a technique described in JP-A-2007-116817, the current is estimated on the basis of an integrated value of U-phase current (or V-phase or W-phase current) instead of DC bus current. The current estimation algorithm does not contain the periodic function and is simple. However, similarly to the technique described in JP-A-2007-221999, the number of times of detection within the period is reduced at high-speed driving, so that the estimation accuracy is lowered.